Performance venues such as theaters, arenas, concert halls, auditoriums, schools, clubs, convention centers and television studios employ battens or trusses to suspend lighting, scenery, drapery and other equipment which is moved relative to a stage or floor. These battens usually include pipe or joined pipe sections that form a desired length of the batten. The battens can be fifty feet or more in length. To support heavy loads, or where suspension points are spaced fifteen to thirty feet apart, the battens may be fabricated in either ladder, triangular or box truss configurations.
Battens often need to be lowered for exchanging and servicing the suspended equipment. To reduce the power necessary to raise and lower the battens, the battens are often counterweighted. The counterweights reduce the effective weight of the battens and any associated loads.
A number of elevating or hoisting systems are available for supporting, raising and lowering battens. One of the most common and least expensive batten elevating systems is a counterweighted carriage that includes a moveable counterweight for counterbalancing the batten and equipment supported by the batten.
Another common elevating or hoisting system employs a winch to raise or lower the battens. The winch may be either hand or electrically operated. Occasionally, in expensive operations, a motorized winch or hydraulic or pneumatic cylinder device is used to raise and lower the battens.
More recently, modular lift assemblies have been employed to raise and lower battens. An example of a modular lift assembly is shown in FIGS. 1A-1C. In this modular lift assembly 2, a motor 4 is disposed in communication with a drum 6, such that the motor 4 rotates the drum 6. One or more wire cables 8 are wound around the drum 6, such that as the drum 6 rotates, the cables 8 are selectively wound about, or advanced from, the drum 6. A plurality of pulleys 10 are disposed to reroute and redirect the cables 8 as they are extended from the drum 6. In this manner, the cables 8 extend generally horizontally from the lift assembly 2 before being rerouted vertically to attachment points on a batten 12 to be raised or lowered. The lift assembly 2 can also include a frame 14 that houses the drum 6 and motor 4, as well as other components included in the lift assembly 2. The frame 14 is preferably mountable to I-beams (or similar support structures) 16 native to the arena in which the lift assembly 2 is to be used.
Modular lift assemblies 1, such as those shown in FIGS. 1A-1C, have revolutionized the way in which battens 12 are raised and lowered. However, because the frame 14 is normally suspended from I-beams or other support structures, the frame 14 is required to withstand a vertical load caused by the weight of the assembly 2 and the weight of the object to be raised or lowered. Moreover, when the wire cables 8 are lead horizontally from the lift assembly 2 and then dropped vertically to the batten 12, the assembly 2 is also subject to a horizontal load. The vertical and horizontal loads may result in sagging or drooping at positions furthest from the support structures and relative bending with respect to the support structure 16 nearest the end of the lift assembly 2 from which the cables 8 extend. These loads are further exacerbated when the weight of the battens 12 is increased and when the distance between points at which the lift assembly 2 is attached to the support structure is increased.
Such loads may result in deformations of the lift assembly 2, which may maliciously affect components of the lift assembly 2. For example, a shaft (not shown) driven by the motor 4 to rotate the one or more drums 6 about which the cables 8 are wound, may be up to seven feet in length, and even slight bending thereof may cause misalignment of the shaft with respect to bearings (not shown) in which the shaft rotates. As a result, a wobble of the rotating components with respect to each other can be created, potentially shortening the life of the bearings, shaft, and/or drums, and increasing noise created by the lift assembly.